Unary Association - modelint/shlaer-mellor-metamodel GitHub Wiki
The Unary Association models the ‘symmetric reflexive relationship’ described in Section 4.2 of [OOA96].
The term ‘unary’ means that there is only one Perspective on this type of Association. As a consequence, all Unary Associations are reflexive (on a single Class). A reflexive (single Class) Association is not necessarily Unary, however. So it is the number of Perspectives that matters.
Here is an example of a Unary Association:
